1. Field of the Invention
The present invention relates to a decorative sheet to be stretched and attached onto the surface of an object, and also relates to a formed product and a transportation apparatus decorated with such a decorative sheet.
2. Description of the Related Art
Various formed products are used as exterior members for a transportation apparatus such as a car. Those formed products have been decorated by painting in many cases. A painted exterior member should have weather resistance and damage resistance that are high enough for the product to withstand long-term usage outdoors.
To provide sufficient weather resistance and damage resistance to an exterior member, a “top coating” technique is often adopted in the field of car painting. According to the top coating technique, the uppermost surface of a painted exterior member is coated with an acrylic resin or a fluorine resin, for example, thereby increasing its weather resistance and damage resistance.
Meanwhile, it was recently proposed that a decorative sheet be attached to the surface of a formed product as a technique of decorating a formed product as disclosed in Japanese Laid-Open Patent Publication No. 2005-153351.
FIG. 9 shows an example of the decorative sheet. The decorative sheet 110 shown in FIG. 9 includes a base member 1 of a resin material and a decoration layer 2 formed on the principal surface 1a of the base member 1 by printing a pattern on that surface 1a with ink, for example. By attaching this decorative sheet 110 to the surface of the body 121 of a formed product in the order shown in FIGS. 10A, 10B and 10C with an adhesive 8 applied on the decoration layer 2, a formed product 120 with a decorated surface can be obtained.
The formed product 121 shown in FIG. 10A includes a hemispherical (cuplike) raised portion 121a and therefore has a rugged surface. For that reason, the decorative sheet 110 being attached is stretched so as to follow such ruggedness perfectly. To stretch the decorative sheet 110 just as intended, the decorative sheet 110 is typically heated and softened before being attached.
A formed product with a decorative sheet can be recycled more easily than a formed product with a painted surface. In addition, a decorated product can have a different type of fine appearance from that of a painted product. That is why a decorative sheet contributes to improving the appearance of formed products noticeably. For these reasons, a method using a decorative sheet is very useful.
If a decorative sheet is used to decorate an exterior member, however, the ink contained in the decoration layer might be deteriorated by UV rays included in sunlight. For that reason, the weather resistance of a decorative sheet needs to be increased.
Japanese Laid-Open Patent Publication No. 2004-250581 discloses a stack of resin layers with good weather resistance. FIG. 11 illustrates such a stack 210 of resin layers.
As shown in FIG. 11, the stack 210 of resin layers includes a base member 211 made of polycarbonate, an acrylic resin layer 212 with a UV absorbent material, and a cured layer 213 formed by curing a coating agent in which a number of ingredients are compounded so as to have a particular composition. These members and layers are stacked in this order one upon the other.
This stack 210 of resin layers realizes high weather resistance because the UV absorbent material included in the acrylic resin layer 212 absorbs UV rays.
However, the present inventors discovered and confirmed via experiments that even when a stack 210 of resin layers as disclosed in Japanese Laid-Open Patent Publication No. 2004-250581, was actually used as a decorative sheet and attached to a formed product by the technique disclosed in Japanese Laid-Open Patent Publication No. 2005-153351, supra, it was difficult in fact to realize sufficiently high weather resistance. This is because the decorative sheet being attached is stretched that its thickness is reduced. If the acrylic resin layer 212 has a reduced thickness, then the amount of the UV absorbent material contained per unit area of the decorative sheet decreases. As a result, UV rays cannot be absorbed sufficiently and the weather resistance decreases.
To overcome such a problem, the overall decorative sheet may be thickened in advance because the decorative sheet is supposed to be stretched and have a reduced thickness eventually. However, the decorative sheet being attached to a formed product is not stretched uniformly everywhere. That is to say, the decorative sheet is stretched to different degrees from one portion of the sheet to another. For that reason, if the entire sheet were thickened, then a portion that would be thick enough even without being thickened that way should be too thick to avoid a significant increase in cost.
Only the acrylic resin layer 212 including the UV absorbent material could be thickened. Actually, however, the acrylic resin layer 212 cannot be stretched so easily as the base member 211 of polycarbonate. That is why the thickened acrylic resin layer 212 could crack when stretched.